1. Field of the Invention
The invention relates to a system for detecting knock or misfire in a cylinder or cylinders of an internal combustion engine. In one of its aspects, the invention relates to a knock or misfire detection system using a single acceleration sensor associated with the engine block. In another of its aspects, the invention relates to a knock or misfire detection system applying digital signal processing technology and discrete wavelet transform algorithms to determine which cylinder or cylinders are exhibiting knock or misfire characteristics.
2. Description of the Related Art
Electronic engine control systems can best adapt to the operating conditions existent in an internal combustion engine when the electronic control system is supplied with current and valid information regarding the operating conditions within the engine. Primary considerations for the operating conditions within the engine include the fuel-air mixture and the timing of an electric spark provided to ignite the compressed fuel-air mixture within each of the cylinders of an internal combustion engine. A mistimed spark or inadequate spark can contribute to knocking in the engine or misfire, respectively. At issue are the methods and means by which the electronic control system is provided with valid information not only for the engine as a whole but for each cylinder of the engine which can independently experience knock or misfire.
Methods of detecting conditions within the engine have been proposed that include optical sensors, pressure sensors, vibration sensors and sensors of electrical characteristics for the ignition system.
Vibration sensors can provide some of the least intrusive methods of gathering data about engine combustion but are subject to providing misleading data due to vibrations generated by the engine and not related to knock or misfire and potentially masking the combustion event in question. Combustion noise is regarded as one of the major factors contributing to engine vibrations. Combustion noise radiates through the engine structure as a direct result of the rapidly changing pressures in the combustion chambers. This combustion noise can include noise generated by piston slap, timing gear impacts, bearing impacts, the fuel system and the valve system. The key to providing useful information to the electronic control system comes in the ability to sort useful vibrations out of the background.
A composite signal from a vibration sensor can be parsed by any number of well-known methods, including a fast Fourier transform. The fast Fourier transform, however, does not give sufficiently differentiated frequency distribution as a function of time to be useful in the electronic engine control system. Wavelet transform analysis, in contrast, can provide frequency distribution information associated with a time scale for use by the electronic control system for association with a given cylinder of the internal combustion engine and with a given position of that cylinder in the internal combustion cycle.
It, therefore, would be advantageous to provide an electronic engine control system incorporating a digital signal processor using wavelet transform analysis to interpret engine vibrations for association with a given type of combustion event in a given cylinder.
The invention relates to a system for detection of combustion anomalies in an internal combustion engine, and includes a crank angle indicator, a vibration sensor, and a digital signal processor. The digital signal processor receives signals from the indicator and the sensor and performs a wavelet transform analysis of the signals from the sensor to develop a vibration frequency signature on a time scale. The digital signal processor then compares the vibration frequency signature to a predetermined value to determine the existence of anomalies in the combustion process, and compares the time scale of the vibration frequency signature to the signal from the indicator to determine which of a plurality of cylinders of the internal combustion engine is exhibiting the combustion anomaly.